1. Field of the Invention
The invention relates generally to a crush box, and more specifically to a technique for preventing a crush box from being displaced to tilt laterally at the time of a short overlap offset collision.
2. Description of the Related Art
There has been proposed a crush box (a) that includes a tubular body having a polygonal section and disposed between an end portion of a bumper beam and a vehicle body in such a posture that the axial direction of the tubular body generally coincides with the longitudinal direction of a vehicle, (b) in which the tubular body has an outer side wall and an inner side wall that is located inward of the outer side wall in the vehicle-width direction, and both the outer side wall and the inner side wall are inclined outward in the vehicle-width direction (i.e., the distance between a line extending in the vehicle longitudinal direction and each of the outer side wall and the inner side wall increases in a direction from the vehicle body toward the bumper beam), and (c) in which the tubular body is crushed into a bellows shape to absorb impact energy as a compressive load is applied to the tubular body from the bumper beam in the axial direction of the tubular body. A crush box described in Japanese Patent Application Publication No. 2010-76476 (JP 2010-76476 A) is an example of the above-described crush box. According to JP 2010-76476 A, a tubular body of the crush box is inclined outward in the vehicle-width direction, and thus the crush box is restrained from being displaced to tilt inward in the vehicle-width direction.
However, in the event of an offset collision, for example, as illustrated in FIG. 5, even the crush box inclined outward in the vehicle-width direction is likely to be displaced to tilt laterally and thus the impact energy absorption performance of the crush box may be lowered. For example, in the case of a short overlap collision between a collision barrier and a bumper beam, that is, a collision with a short (small) overlap between the collision barrier and the bumper beam, as illustrated in a section of a conventional crush box in FIG. 9, an end portion of the bumper beam, which is located outward of the crush box in the vehicle-width direction, undergoes bending deformation and the crush box itself is displaced to tilt inward in the vehicle-width direction from its root (its end portion on the vehicle body side), so that the crush box is not crushed into a bellows shape. As a result, the impact energy absorption performance is significantly lowered. FIG. 9 illustrates the conventional crush box that is disposed so as to extend substantially parallel to the vehicle longitudinal direction as illustrated in FIG. 15. However, even in the case where a crush box inclined outward in the vehicle-width direction as described in JP 2010-76476 A is adopted, a similar problem may occur depending on an angle of inclination of the crush box. If the angle of inclination of the crush box is increased, occurrence of the above-described problem may be reduced but the crush box is more likely to be displaced to tilt outward in the vehicle-width direction. Therefore, it is difficult to select the angle of inclination at which the crush box is displaced to tilt neither inward nor outward in the vehicle-width direction in the event of a short overlap collision.